Platinum(II) Complexes Bearing a Thiolate/Thioether Ligand – Hemilability vs. Dealkylation

Substitution of the chloro ligands of cis ‐[Pt(PEt 3 ) 2 Cl 2 ] by 4‐methylthio‐2‐thioxo‐1,3‐dithiole‐5‐thiolate ( L ) leads to the thiolato complexes trans ‐[Pt(PEt 3 ) 2 Cl L ] ( 2 ) and trans ‐[Pt(PEt 3 ) 2 L 2 ] ( 1 ), which have been characterised by X‐ray crystallography. In the solid state, the square planar arrangement is capped by an endocyclic sulfur atom of L , which gives rise to distorted square‐pyramidal and pseudooctahedral geometries for 2 and 1 , respectively. Complex 1 coexists in solution with [Pt(PEt 3 )(η 1 ‐L )(η 2 ‐L )] ( 3 ), which results from the reversible dissociation of one phosphane ligand. The combination of η 1 ‐(thiolato) and η 2 ‐(thiolato/thioether) L in 3 has been established by variable‐temperature 1 H NMR spectroscopy and crystal structure determination. The η 2 ‐coordination mode of L is also observed in cis ‐[Pt(PEt 3 ) 2 L ] + ( 4 ), which results from the abstraction of the chloro ligand of 2 by excess TlPF 6 . An S ‐demethylation reaction occurs when 1 is heated in acetonitrile to yield the structurally‐characterised dithiolene complex [Pt(PEt 3 ) 2 (dmit)] ( 5 ) (dmit 2– = 2‐thioxo‐1,3‐dithiole‐4,5‐dithiolate) and Me L . Treatment of cis ‐[Pt(PPh 3 ) 2 Cl 2 ] with 2 equiv. of L leads to a mixture of [Pt(PPh 3 ) 2 (dmit)] ( 6 ) and [Pt(PPh 3 )(η 1 ‐L )(η 2 ‐L )] ( 7 ). Complex 7 predominates in solution over its parent compound,[Pt(PPh 3 ) 2 L 2 ]. The identification of CH 3 Cl by 1 H NMR spectroscopy proves that [Pt(PPh 3 ) 2 Cl L ] is involved as an intermediate in the demethylation process. The reaction of L with platinum precursors that are blocked in a cis arrangement by chelation of 1,1‐bis(diphenylphosphanyl)methane (dppm) and 1,1‐bis(diphenylphosphanyl)ethane (dppe) leads to the formation of the thiolato complexes cis ‐[Pt(η 2 ‐dppm) L 2 ] ( 8 ) and cis ‐[Pt(η 2 ‐dppe) L 2 ] ( 9 ). The solid‐state structure of 8 reveals the occurrence of an additional weak interaction between a thiomethyl group and the platinum centre (Pt–S 3.073 Å).